Mattress



FIG. 1 is a perspective view of a mattress;

FIG. 2 is a back end view of the mattress, the front end view being identical thereto;

FIG. 3 is a left side view of the mattress, the right side view being identical thereto; and,

FIG. 4 is a bottom view of the mattress.

The broken line showing of the top and bottom of the mattress is for the purpose of illustrating structure and forms no part of the claimed design. 

CLAIM The ornamental design for a mattress, as shown and described. 